This invention relates to a dry barrel finishing machine and a method of dry barrel finishing, wherein a media and workpieces are flowed in the barrel of the machine for fine abrasive finishing of the workpieces.
Generally, barrel finishing is well known as a method for finely grinding workpieces such as bolts, shafts, bearings, etc. In barrel finishing, a mass, which is comprised of media and workpieces, is charged into a receptacle, i.e. a barrel, and the barrel is activated to flow the mass in it to finish the workpieces through interactive attrition between the workpieces and the media.
Barrel finishing includes dry finishing and wet finishing. Wet finishing uses compounds and water as well as a media, while dry finishing does not use fluid. Wet barrel finishing requires washing and drying workpieces after the finishing as well as water treatment for removing waste attrition fluid and waste washing water. It is well known that a drawback of wet barrel finishing is that it requires a drying apparatus and a fluid treatment device, and therefore it requires more space for these items. Another drawback is that wet barrel finishing takes additional time and labor.
In view of such drawbacks, dry barrel finishing is often used. In dry barrel finishing, however, attrition produces dust and fragments of the media. Further, frictional heat is generated due to the attrition between the workpieces and the media, and between the barrel and the mass. The attrition dust tends to spread out of the barrel and contaminate the environment. The dust also causes clogging in the media, lowering the abrasive ability of the media, and resulting in uneven finishing on the workpieces. Further, in a conventional centrifugal barrel finishing machine, which has an upper immobile tank and a bottom rotary disc, fragments of the media tend to get caught in the space or slit between the rotary disc and the immobile tank. If any fragment becomes jammed in the slit, the rotating disc and the tank are heavily rubbed thereby, and a frictional heat of high temperature will be generated. This heat tends to melt any liners covering the surfaces of the disc and the tank, and as a result, fragments adhere to these liners, thereby hindering the rotation of the disc.
Recently, artificial plastic media have been used as barrel finishes. This plastic media is generally produced by externally heating, in a mold, a mixture of abrasive material and grains of bonding material of an unsaturated polyester resin, a polyvinyl chloride resin, etc. Through this external heating, if the entire mixture is sufficiently heated, a skin layer of the bonding material is formed on the outside of the medium. On the contrary, if the mixture is heated such that only the outside is heated so as to prevent such a skin layer on the surface of the media, the inner part of the media will be brittle because the abrasive material and the bonding material have not been combined sufficiently. This resulting brittle media will cause fragments during barrel finishing, and the fragments will be jammed in the slit of the barrel as described above.
Japanese Patent (Y) 2-43,652 discloses an improved plastic media which is, for example, in the shape of a cylinder. This media is porous and has no skin layer on the outer surface. The media contains abrasive grains combined with the bonding material and pores between the abrasive grains. Since the abrasive grains are separated by pores and are always exposed, they are effective.